This research will aid our understanding of the functional organization and specialization of the cerebral cortex in humans and its role in sensory perception. In particular, it will aid our understanding of primary and nonprimary auditory cortex and of the neurobiological mechanisms underlying the processing of speech sounds. In addition to identifying the neural mechanisms underlying the McGurk effect, which is relevant to much investigation in linguistics and other studies of speech processing, this research will contribute to our understanding of auditory-visual integration processes in normal and atypical speech perception and of more general principles of auditory- visual integration. Additionally, this research will aid our understanding of the fundamental principles of cross-modal integration and multimodal sensory perception, and will identify neuroanatomical substrates and neurobiological mechanisms which may be involved in these processes. The understanding of neurobiological mechanisms of human brain function, and the evolution of these mechanisms is our long-range goal. Ultimately, this research will aid in the understanding of major dysfunctions of speech and hearing such as sensory and phonological aphasia, and will enable us to design and implement more appropriate therapeutic approaches to neurological impairments based upon fundamental principles of speech processing. In addition, employing functional magnetic resonance imaging (fMRI) to identify neural mechanisms of speech perception permits both the direct correlation of function with anatomy and repeated studies in the same individual. Thus, it will undoubtedly prove to be extremely useful in presurgical mapping, determining hemispheric dominance in epilepsy patients, and monitoring recovery from stroke or cerebral trauma. Additionally, the use of fMRI in these experiments would aid in establishing this methodology as a powerful clinical tool, an application that would have a profound impact on clinical care.